Evaporation crucible

ABSTRACT

An evaporation crucible comprising an elongated tubular portion having a single slot or a series of evenly spaced elongated slots at the top surface of said tubular portion. A series of continuous compartments are located at the internal bottom surface of the tubular portion with a series of plates evenly dividing said compartments.

United States Patent 11 1 Erhart et al.

1451 July 17, 19737 EVAPORATION CRUCIBLE [75] Inventors: Francis J. Erhart, Webster; Carl B.

Fisher, Mendon, both-of NY.

[73] Assignee: Xerox Corporation, Stamford, Conn. 221 Filed: Dec. 20, 1971 [2]] Appl. No.: 209,608

[52] US. Cl. 432/263 [5i] Int. Cl. F27b 21/04 [58] Field of Search 263/47, 48; 266/39; 432/258, 262, 263

[56] Reierences Cited UNITED STATES PATENTS Zucchinelli 266/39 964,871 7/1910 Johnson 263/47 R Primary E.irdminer-John J .Camby Attorney-James J. Ralabate s71 ABSTRACT An evaporation crucible comprising an elongated tu bular portion having a single slot or a series of evenly spaced elongated slots at the top surface of said tubular portion. A series of continuous compartments are located at the internal bottom surface of the tubular portion with a series of plates evenly dividing said compartments.

5 Claims, 7 DrawingFigures PAIENTE JUL 1 7 ms FIG. IA

FIG. IB

INVENTORS FRANCIS J. ERHART CARL B.-FISHER ATTORNEY EVAPORATION CRUCIBLE BACKGROUND OF THE INVENTION The instant invention relates to vacuum coating apparatus more specifically to an evaporation crucible.

Generally, in the practice of evaporating relatively thin films or layers of metals or non-metals onto suitable substrates, the crucible or evaporator vessel commonly employed comprises an open boat having a somewhat rectangular cross section. In the use of such boats or crucibles, the spit and spatter of both dirt and the material to be coated can result in numerous defects which occur on the surface of the final coated substrate. The spit and spatter effect is caused by the bubbling of the liquid evaporant material during initial evaporation, resulting in tiny droplets from the bubbling surface ending up on the substrate surface. Because of this problem, it is necessary to space the location of the crucible at relatively long distances from the substrate to be coated. This requirement places some undesirable constraints on the design of coating apparatus, especially when coating is carried out under a high vacuum. I

In addition to the above problems, with open boat type crucibles, there is little or no control of the incident angle of the evaporant material deposited onto a coated substrate.

The above problems are particularly relevant to vacuum evaporation techniques which are used in forming photoconductive coatings on the surface of metallic drums or plates which are used as the photosensitive member in xerography.

There is, therefore, a need in the art for improved crucible apparatus which allows closer spacing between the crucible and substrate, thereby improving the efficiency of the evaporation cycle, and for better control or reduction of spit and spatter which causes surface defects on coated substrates.

OBJECTS OF THE INVENTION SUMMARY OF THE INVENTION The foregoing objects and others are accomplished in accordance with this invention by providing a novel evaporation crucible. Generally, the cross section of the crucible may be of any suitable shape such as a hollow circular or rectangular tube, and includes single as well as a plurality of slots running along the length of the top or side. These slots may have a fixed or constant width along the entire length of the crucible or may vary in width. The inside tube portion of the crucible contains a series of bottom plates or dams which effectively breakup the crucible into a plurality of sections.

The crucibles of the present invention are usually used with direct resistance heating in which a high current is passed throughthe crucible, which is usually a metal or other conductivematerial, with electrical connections being maintained at each end of the crucible. Generally, the lighter the gauge of the metal, the lower the current or power requirements. The crucibles of the present invention are applicable to evaporating metals or non-metals for any suitable use, but have particular utility for the formation of photoconductor coatings for use in xerography, and more specifically, for the deposition of selenium and selenium alloys onto a supporting substrate such as a metallic drum, plate or flexible substrate.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages of the instant invention will become apparent upon consideration of the following disclosure of the invention, especially when taken in conjunction with the accompanying drawings'wherein:

FIGS. 1A and 1B illustrate top view of two embodiments of crucible apparatus of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS A top view of the two embodiments of the instant invention are schematically illustrated in FIGS. 1A and 18. FIG. 1A represents a top view of one embodiment of a crucible of the instant invention. The crucible comprises an elongated metallic tube 1 1, containing a thin elongated slot 12, at the top surface. FIG. 1B illustrates a top view of a second embodiment of the invention and comprises an elongated metallic tube 1 1, containing a plurality of slots 12, at the top surface.

A preferred embodiment of an evaporation crucible of the instant invention is set forth in FIG. 2. Reference character 10 represents a vacuum evaporation crucible formed by a hollow metal tube 11, containing a plurality of open slots 12 evenly spaced atthe top surface of the tube. Below each slot at the bottom of tube 11, are formed a plurality of compartments 14, directly below and centered beneath each slot. The compartments are separated by a series of plates or dams 15. The tube 11 is sandwiched by two metal end plates 16 and 17 to which suitable electrical heating connections may be affixed and by which the crucible may be mounted upon any suitable support or bracket.

FIG. 3 illustrates a schematic sectional end view of the apparatus of FIG. 2 illustrating the relative height of dam member 15 as opposed to the overall diameter of tube 11. I

In operation, the tube is loaded with the appropriate source of evaporant, and in its preferred utility, a charge of a selenium or selenium alloy suitable for use in forming a photoconductor coating on a xerographic plate or drum. The charge or evaporant material is uniformly dispersed within cavities 14 of each section. The crucible is normally resistance heated by passing a high current through themetal comprising the tube with electrical connections being mounted at each end plate. One suitable material for the tube comprises Type 304 stainless steel, but any other suitable metal may be used. In order to insure uniformity of the coating thickness, it has been found that the height of dams an end view of the apparatus of,

of the present invention comprises placing a drum in the form of a hollow metallic cylinder over each slot, and rotating the drum above said slot while the crucible is heating and the evaporant material such as selenium or selenium alloy is evenly coating over the rotating drum surface.

In order to obtain uniform heating and evaporation of the evaporant material, it is preferred that a suitable unused or dead space must be provided at each end of the tube crucible. This dead space is illustrated by reference character 18 (FIG. 2) and comprises a space which is not used for any evaporant charge. It has been found that without the inclusion of this dead space in the tube crucible configuration of the present invention, that uneven heating at the end of the crucible results, and the overall efficiency of the crucible with regard to evaporating all of the material uniformly is greatly reduced.

FIG. 4A, 4B and 4C are end views of a crucible and drum substrate arrangement and illustrate three embodiments of Applicants invention. FIG. 4A illustrates the embodiment previously described in which crucible 20 has a slot or slots 21 at the top surface. The arrow illustrates the direction of vapor flow to the surface of the drum 22. FIG. 48 illustrates the simultaneous coating of two drums 33 and 34 from slots 31 and 32 at the upper side surface of crucible 30. FIG. 4C illustrates a further embodiment of the present invention in which drums 43 and 44 are simultaneous coated from side slots 41 and 42 of crucible 40. It should be understood that when coating drums, that the drum is continuously rotated during the evaporation cycle.

It will be evident that several variations in the shape would appear .to those skilled inthe art. For example,

of the overall crucible apparatus may be made and it to other geometric configurations including rectangles and variations thereof. The essential features, however, include a single or plurality of evenly placed slots, the compartmenting of the bottomof the crucible through the use of dams, and the ratio of dam height to the internal dimensions of the crucible.

Other modifications and ramifications of the present invention would appear to those skilled in the art upon reading the disclosure. These are also intended to be within the scope of this invention.

What is claimed is:

1. An evaporation crucible comprising a central tubular portion having a series of evenly spaced elongated slots at the top surface of said tubular portion, a series of continuous compartments located at the bottom of said tubular portion, with a series of dams evenly dividing said compartments, with the height of said dams being a maximum of about one-fourth that of the radius of the tubular portion, a section at each end of said tubular portion which is not utilized for evaporation, and a plate at either end of said tubular portion of said crucible.

2.-The crucible of claim I in which a single slot runs the length of the top surface.

3. The crucible of claim 1 which a plurality of slots are located along at least one side of the tubular portion of thecrucible.

4. The crucible of claim 1 in which at least one longitudinal slot is located along opposite sides of the tubular portion of the crucible.

5. The crucible of claim 1 in which at least one longitudinal slot is located at opposite sides of the tubular from the vertical.

# i t i 

1. An evaporation crucible comprising a central tubular portion having a series of evenly spaced elongated slots at the top surface of said tubular portion, a series of continuous compartments located at the bottom of said tubular portion, with a series of dams evenly dividing said compartments, with the height of said dams being a maximum of about one-fourth that of the radius of the tubular portion, a section at each end of said tubular portion which is not utilized for evaporation, and a plate at either end of said tubular portion of said crucible.
 2. The crucible of claim 1 in which a single slot runs the length of the top surface.
 3. The crucible of claim 1 which a plurality of slots are located along at least one side of the tubular portion of the crucible.
 4. The crucible of claim 1 in which at least one longitudinal slot is located along opposite sides of the tubular portion of the crucible.
 5. The crucible of claim 1 in which at least one longitudinal slot is located at opposite sides of the tubular portion of the crucible at an angle approximately 90* from the vertical. 